During vertebrate neural development, generation of cellular diversity depends upon activation of signal transduction pathways and expression of genes encoding transcription factors that regulate the formation of neurons and glia from multipotent progenitor cells. Many cell-autonomous factors involved in neuronal cell fate specification have been described; however, determinants of astrocyte lineage development from mutipotent precursors are poorly understood. Several lines of evidence indicate roles for Epidermal Growth Factor Receptor (EGFR)-mediated signaling in this process, and activating mutations of EGFR are implicated in the progression from low-grade astrocytoma to high-grade glial brain tumors in humans. This proposal will test the hypothesis that common mechanisms may underlay aspects of astrocyte development and tumorigenesis. In preliminary work, we have established an in vitro model of astrocyte development from multipotent neural stem cells (NSC). We show that exogenous EGFR proteins can stimulate mature astrocytes to re-enter the cell cycle efficiently in the setting of INK4a deficiency, a mutation commonly found in high-grade human brain tumors. These preliminary results together with previously published data suggest that EGFR signaling is a powerful regulator of astrocyte differentiation that may act in concert with other synergistic genetic aberrations in the generation of transformed glia. Specific Aim 1 is to determine roles for EGFR signaling in survival, proliferation and differentiation along the neural stem cell (NSC)-to-astrocyte axis in wild type and INK4a deficient genetic backgrounds. Specific Aim 2 is to determine molecular consequences of EGFR activation along the NSC-astrocyte axis using biochemical and expression profiling approaches. Specific Aim 3 is to use genetic profiling information from Aims 1 and 2 to identify transcription factors with functional roles during astrocyte lineage development in the mammalian CNS. In Specific Aim 4, genes identified in Projects 1-3 will be subjected to a functional screen to identify factors involved in glial cell cycle regulation and transformation in vitro and in vivo.